You seem to be missing the obvious. Given that the room/speaker completely dominates the response below transition, the speaker designer can only do so much, perhaps a "best guess' as to what the exact roll off/shape should be. Regarding what you can/can't hear with "hideous" bumps is another matter entirely, at best, yet another confounder not in the domain of speaker designer. No one sensible argues against EQ below the transition frequency where room and placement dominates.Many of the comments keep referring to the specific measured response for particular speakers in particular rooms. Of course I know these are filled with many hideous looking bumps that are nevertheless, not that audible (I've made measurements - I was horrified the first time)!
What I was hoping for was a discussion, and perhaps general consensus, on (approximately) what speaker designers should be aiming for at the bass roll-off of the main speakers?